Upgrading to S4 Brakes
Older 928's can get increased stopping power by replacing the brakes with the larger S4 ones. I recently upgraded my 78 928 to S4 brakes all around. The following is a list of parts you WILL require...
-4 S4 calipers
-4 S4 or equivalent brake rotors (W pads)
On the front end...
-2 S4 lower ball joints (If you are using the early aluminum ball joints you will also require an additional eccentric adjuster)
-L.H. + R.H. spindle and brake caliper mount (steering knuckle)
-2 Brake lines from the S4 calipers to the inner fender
On the rear end...
You have two ways to go..
1st way (cheapest , but perhaps not as good)
-2 brake lines from the caliper to the inner body
-4 5mm spacers (to space the caliper into the car more to line up properly with the disc.)
-(recommend)2 30mm+ studded "Hub centric" wheel spacers (The rims sit noticeably further in when compared to the front, NOTICABLY!)
2nd way (More expensive but probably better)
-2 Brake lines
-2 rear S4 hubs
-2 complete rear axles
(I don't know how far out the rims will sit in the rear since I did not go this route)
From an application point of view..
-If you are going to be club racing then you should NOT use the Phone Dial rims because of a clearance issue between the face of the caliper and the outer facing face of the rim, not a diameter issue I had originally thought of. Of course if you are going racing you probably will have a different set of rims!
-If you are using the car as either a daily driver or only plan on autoXing the car they should be excellent!
There is enough room between the caliper and the rim for the everyday type guy, about 3.8mm near the center of the rim at the closest point. You might say that 3mm isn't enough, but it is right at the hub of the rim where flex is at a minimum, however I wouldn't want to test that on any club racing events! But for autoX and the street it's fine.
-Options to upgrade to (if you can afford it)
-Most important upgrade would probably be the S4 master cylinder. (However I am using my stock 78 one and contrary to popular belief my 78 one works perfectly. No spongy pedal or lack of braking feed back on the pedal. The only thing to watch out for is NOT to fill the reservoir to MAX, but rather about 3/4 to MAX. I think from heat expanding the fluid under race situations it will over flow and spray on your hood
-Install S4 lower front A arms, they have the added holes for a air scoop to work with the "S" spoiler air rams. (You may also then be required to install the upper A arm as well, due to a possible change in length. I don't know if they are the same length.)
That's about it. If you have any questions ask away. Personally though, I don't think the late model master cylinder is worth the money and hassle to put in, unless you are going to the races with the car, or you have the money just itching to be spent!
Installing S4 front brakes on early 928 requires upper ball joint arms in order to correct extreme positive camber. You do not have enough adjustment on the lower ball joints to correct the camber. The upper arms are a few millimeters longer on S4's. Then, if you use the original wheels, you need 5mm spacers to clear the calipers. This leaves adequate clearance for stock 225/60/16 tyres.
The rear conversion requires a little more thought. Use S4 hubs - with the longer wheel studs they go straight onto the splined axle shafts. The Brembo caliper will need a spacer fabricated between the swingarm and the caliper lugs (approx 4mm thick) in order to center the rotor. Use the old front caliper bolts (shortened a little) to fasten down the new calipers to the swingarm. Forget about the back plates, they won't fit. Then put the stock S4 wheel spacer on and fit factory wheels and tyres.
Use Goodridge S4 brake hoses and have a 4 wheel alignment. This leaves you with a wider rear track (by 50mm) and no clearance problems. I did this on my 1978 928, using 1987 928 S4 parts. Of course I used the lower S4 front arms and hubs. Also, don't forget to throw away the A.B.S. sensors.
928 Tips Home Greg's Home